Recently, as an input detection device, an input detection device having a touch detection function capable of detecting proximity (hereinafter, including contact) of an external object, so-called a touch panel, has drawn attention. The touch panel is mounted on a display device such as a liquid-crystal display device or integrated with a liquid-crystal display device and is provided as a display device with a touch detection function.
There is a touch panel which enables use of a pen, for example, as the external object. By using the pen, for example, a small region can be designated, and handwritten characters can be input. There are various techniques for detecting touch by the pen. One of the various techniques is an electromagnetic induction method. In the electromagnetic induction method, since it is possible to realize high accuracy and high pen-pressure detection accuracy and to also realize a hovering detection function of detecting a hovering state in which the external object is spaced apart from the front surface of the touch panel, the electromagnetic induction method is an effective technique as a technique to detect touch by the pen.
Also, there is a touch detection device capable of detecting a finger or the like as the external object. In this case, since the detection target is different from the pen, a method different from the electromagnetic induction method is employed as a technique to detect touch. For example, there is a method in which an optical change, a resistance value change, or an electric field change generated by touch of a finger or the like is detected. Among these methods, the method of detecting an electric field change includes, for example, a capacitive sensing method using an electrostatic capacitance, for example. Since the capacitive sensing method has a comparatively simple structure and low power consumption, it is used in PDA (personal digital assistance), etc.
A technique related to a touch panel of the electromagnetic induction method is described in Japanese Patent Application Laid-Open Publication No. H10-49301 (Patent Document 1), for example.